Small scale actuators and methods for their formation and use

ABSTRACT

An actuator assembly and method for making and using an actuator assembly. In one embodiment, the assembly includes an actuator body having an actuator channel with a first region and a second region. An actuator is disposed in the actuator channel and is movable when in a flowable state between a first position and a second position. A heater is positioned proximate to the actuator channel to heat the actuator from a solid state to a flowable state. A source of gas or other propellant is positioned proximate to the actuator channel to drive the actuator from the first position to the second position. The actuator has a higher surface tension when engaged with the second region of the channel than when engaged with the first region. Accordingly, the actuator can halt upon reaching the second region of the channel due to the increased surface tension between the actuator and the second region of the channel.

TECHNICAL FIELD

[0001] The present invention is directed toward small actuators fordevices such as valves, and methods for forming and using suchactuators.

BACKGROUND

[0002] Microvalves are miniature valves used to control fluid flows atlow flow rates. Such valves and other micro-electromechanical (MEMS)devices are conventionally used in several industrial and professionalapplications where it is important to precisely regulate the flow ofsmall quantities of gases or liquids. For example, microvalves are usedfor some types of medical research (such as DNA research), medicaltreatments, and other types of applications that involve metering fluidsat low flow rates.

[0003] Some conventional microvalves are formed directly in asemiconductor substrate (such as silicon) using techniques generallysimilar to those used to form integrated circuits. Such valves typicallyinclude a flexible diaphragm that opens and closes a fluid orifice whenselected voltages are applied to the valve. Examples of such valves aredisclosed in U.S. Pat. No. 5,810,325 to Carr, which is incorporatedherein in its entirety by reference.

[0004] One drawback with some conventional diaphragm microvalves of thetype described above is that the valves may fail because the diaphragmcan fracture or deform after repeated uses. Another drawback is thatconventional diaphragms typically do not exert a large sealing force toclose the fluid orifice. Accordingly, such diaphragms may not besuitable for valves that regulate high pressure fluids.

SUMMARY

[0005] The present invention is directed toward actuators and methodsfor forming and using actuators. An actuator assembly in accordance withone aspect of the invention includes an actuator body having an actuatorchannel with a first end and a second end spaced apart from the firstend. An actuator is disposed in the actuator channel and is movable whenin a flowable state from a first position in the actuator channel to asecond position in the actuator channel. Accordingly, the assembly canfurther include a heater positioned proximate to the actuator channel toheat the actuator from a solid state to a flowable state. In a furtheraspect of the invention, the actuator body can include a fluidpassageway having an orifice in fluid communication with the actuatorchannel. Accordingly, the actuator can allow fluid to flow through theorifice when the actuator is in the first position and block the flow offluid through the orifice when in the second position.

[0006] The invention is also directed toward a method for manufacturingan actuator. In one aspect of the invention, the method can includeforming a channel in a substrate, positioning an actuator in the channelwith the actuator being movable within the channel between a firstposition and a second position when the actuator is in a flowable state,and disposing an actuator heater adjacent to the channel with theactuator heater configured to at least partially liquify the actuator.The method can further include forming the channel to have a firstregion and at least one second region adjacent to the first region. Thefirst region can have a first surface characteristic, and the secondregion can have a second surface characteristic different than the firstsurface characteristic. The actuator can have a first surface tensionwhen in a flowable state and contacting the first region, and theactuator can have a second surface tension when in a flowable state andcontacting the second region. The second surface tension can be greaterthan the first surface tension such that the actuator can halt itsmovement through the channel upon contacting the second region.

[0007] The invention is also directed toward a method for controlling anactuator. The method can include heating the actuator in an actuatorchannel from a solid state to a flowable state, moving the actuator in afirst region of the actuator channel from a first position to a secondposition, and cooling the actuator to solidify the actuator in a secondposition. The method can further include halting the motion of theflowable actuator at the second position by engaging the actuator with asurface of a second region of the channel. For example, the actuator canhave a surface tension when in contact with the second region that ishigher than a surface tension of the actuator when in contact with thefirst region such that the actuator can halt its movement in the channelupon contacting the second region.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a partially exploded top isometric view of an actuatorassembly in accordance with an embodiment of the invention.

[0009]FIG. 2 is a cross-sectional side view illustrating a process fordepositing an actuator on a portion of the assembly shown in FIG. 1 inaccordance with an embodiment of the invention.

[0010] FIGS. 3A-3B are cross-sectional side views illustratingadditional processes for forming the actuator shown in FIG. 2 inaccordance with an embodiment of the invention.

[0011]FIG. 4 is a top isometric view of a portion of an assembly havingan actuator with a slider portion in accordance with another embodimentof the invention.

[0012]FIG. 5 is a partially schematic view of a valve assembly inaccordance with yet another embodiment of the invention.

DETAILED DESCRIPTION

[0013] The present disclosure describes actuators, such as valveactuators, and methods for making and using such actuators. Manyspecific details of certain embodiments of the invention are set forthin the following description and in FIGS. 1-5 to provide a thoroughunderstanding of these embodiments. One skilled in the art, however,will understand that the present invention may have additionalembodiments, or that the invention may be practiced without several ofthe details described below.

[0014]FIG. 1 is a partially exploded top isometric view of an actuatorassembly 10 formed in accordance with an embodiment of the invention. Inone aspect of this embodiment, the assembly 10 is configured to regulatea flow of fluid (liquid, gas or another flowable substance) through afluid passageway 30. Accordingly, the assembly 10 can include a body 11having a first portion 11 a that houses the fluid passageway 30 and asecond portion 11 b attached to the first portion 11 a. The firstportion 11 a can include an actuator or piston 50 that slides within anactuator channel or piston channel 20 to either open or close a segmentof the fluid passageway 30.

[0015] In one embodiment, the body 11 can be formed from a semiconductormaterial, such as silicon. Accordingly, the features formed in the body11 can be formed using techniques generally similar to thoseconventionally used for forming integrated circuits in semiconductorsubstrates, as described in greater detail below. In other embodiments,the body 11 can be formed from non-semiconductor materials and/or withother techniques. In either embodiment, many of the features of the body11 can be formed separately in the first portion 11 a and the secondportion 11 b. The portions 11 a, 11 b can subsequently be joined byattaching an upper surface 12 of the first portion 11 a to a lowersurface 14 of the second portion 11 b. Accordingly, the first portion 11a can include a bonding layer 13 to promote adhesion between the firstportion 11 a and the second portion 11 b. Alternatively, the secondportion 11 b can include a bonding layer in addition to or in lieu ofthe bonding layer on the first portion 11 a, or the bonding layer 13 canbe eliminated.

[0016] In one embodiment, the channel 20 in the body 11 can include abottom surface 21 and opposing side surfaces 22 in the first portion 11a, and a top surface 23 in the second portion 11 b. Accordingly, thechannel 20 can be completely enclosed when the second portion 11 b isjoined to the first portion 11 a. In one aspect of this embodiment, theside surfaces 22 can be perpendicular to the bottom surface 21.Alternatively, the side surfaces 22 can be canted relative to the bottomsurface 21. In either embodiment, the channel 20 can have a firstunwetted region 25 a (shown by left cross-hatching) toward a first end26 of the channel 20, a second unwetted region 25 b (shown by rightcross-hatching) toward a second end 27 of the channel 20, and a wettedregion 24 between the first and second unwetted regions 25 a, 25 b. Thefluid passageway 30 intersects the channel 20 in the wetted region 24.Accordingly, the fluid passageway 30 can have an entrance orifice 31 inone side surface 22 of the channel 20 and an exit orifice 32 in theopposite side surface 22.

[0017] The actuator 50 is positioned in the wetted region 24 proximateto the entrance orifice 31 and the exit orifice 32. When the actuator 50is in a liquid state (or another flowable state), it can wet and sealagainst the bottom surface 21, the side surfaces 22 and the top surface23 of the channel 20. The actuator 50 can also move back and forth alongthe wetted region 24, as indicated by arrows “A” and “B,” when in theflowable state to close and open the entrance orifice 31.

[0018] In a further aspect of this embodiment, the actuator 50 will notmove into either of the unwetted regions 25 a, 25 b due to highcapillary forces associated with the interface between the actuator 50and the unwetted regions 25 a, 25 b. Accordingly, the motion of theactuator 50 can be limited to linear travel between a first position anda second position. In the first or open position (shown in FIG. 1), theactuator 50 is spaced apart from the entrance orifice 31 and the exitorifice 32 of the fluid passageway 30 to allow fluid to pass through thefluid passageway 30 from the entrance orifice 31 across the channel 20to the exit orifice 32. In the second or closed position, the actuator50 is positioned between the entrance orifice 31 and the exit orifice 32to block the flow of fluid through the fluid passageway 30 beyond theentrance orifice 31.

[0019] In one aspect of an embodiment of the assembly 10 shown in FIG.1, the actuator 50 can be moved back and forth within the channel 20 bysequentially introducing a gas toward one of the first end 26 or thesecond end 27 of the channel 20. For example, the assembly 10 caninclude two gas sources 40 shown in FIG. 1 as a first gas source 40 atoward the first end 26 and a second gas source 40 b toward the secondend 27. In a further aspect of this embodiment, each gas source 40 caninclude a metal hydride that releases hydrogen when heated and reabsorbsthe hydrogen when cooled. Accordingly, the first gas source 40 a can beheated to release hydrogen into the channel 20 toward the first end 26and drive the actuator 50 toward the closed position, as indicated byarrow A. Alternatively, the second gas source 40 b can be heated torelease hydrogen toward the second end 27 of the channel 20 and drivethe actuator 50 toward the open position, as indicated by arrow B.Additional materials relating to metal hydrides and other gas-containingmetals are included in Chapter 8 of “Scientific Foundations of VacuumTechnique,” by S. Dushman and J. M. Latterly (1962), and in pending U.S.patent application Ser. Nos. 09/546,084 and 09/258,363, all incorporatedherein in their entirety by reference.

[0020] In one embodiment, the body 11 can include vent channels 43coupled to the gas sources 40 and/or the channel 20. The vent channels43 can provide a safety outlet for hydrogen at the gas source 40 and/orin the channel 20 to vent the hydrogen if the pressure of the hydrogenexceeds a preselected value. The vent channels 43 can also dampenpressure pulses produced by the gas sources 40 by receiving some of thegas released by the gas sources 40. Alternatively, the vent channels 43can release the hydrogen produced by the gas sources 40 from theassembly 10 during normal operation. Accordingly, the hydrogen is notreabsorbed by the gas sources 40. In a further aspect of this alternateembodiment, the gas sources 40 can be used for a limited number ofactuator movements, or the gas sources 40 can be replenished with gasfrom an external source.

[0021] In yet another aspect of an embodiment of the assembly 10 shownin FIG. 1, the body 11 can include one or more heaters for controllingthe temperature of the gas sources 40 and/or the actuator 50. Forexample, the body 11 can include gas source heaters 41 adjacent to andthermally coupled to each of the gas sources 40 to independently heatthe gas sources 40 and release the hydrogen (or other gas) from the gassources 40. The body 11 can further include an actuator heater 42positioned adjacent to and thermally coupled to the wetted region 24 ofthe channel 20 to heat and at least partially liquify the actuator 50prior to moving the actuator 50 within the channel 20. The heaters canbe independently controlled to achieve the temperature necessary torelease gas from the gas sources 40 and at least partially liquify theactuator 50 at selected phases during the operation of the assembly 10,as will be described in greater detail below. The heaters can bepositioned in the first portion 11 a of the body 11 (as shown in FIG. 1)or alternatively, the heaters can be positioned in the second portion 11b.

[0022] The materials forming channel 20 and the actuator 50 can beselected to enhance the performance of the actuator 50 in the channel20. For example, the wetted region 24 of the channel 20 can include acoating of a noble metal (such as platinum or gold), or another metal(such a palladium or rhodium) that resists corrosion and/or is easilywetted by the actuator 50 when the actuator 50 is in an at leastpartially flowable state. The actuator 50 can accordingly include amaterial that has a relatively low melting point and that readily wetsthe wetted region 24. Suitable materials for the actuator 50 includelead and lead alloys (such as are found in solders), bismuth, cadmium,selenium, thallium, tin and/or zinc. In other embodiments, the actuator50 can include other metals, alloys, inorganic and/or organic materials,so long as the actuator 50 can achieve an at least partially flowablestate when heated and/or can be halted by contact with the non-wettedregions 25 a, 25 b. Conversely, the non-wetted regions 25 a, 25 b of thechannel 20 can be coated with a material that is not easily wetted bythe actuator 50. For example, when the actuator 50 includes lead or alead alloy, the non-wetted regions 25 a, 25 b can include an oxide or anitride, such as silicon dioxide, aluminum oxide, or silicon nitride. Inany of these embodiments, the materials selected for the body 11, thewetted region 24 and the non-wetted regions 25 have a higher meltingpoint than the material selected for the actuator 50 so that only theactuator 50 will melt when the actuator heater 42 is activated.

[0023] In operation, the fluid passageway 30 is coupled to a source offluid (not shown in FIG. 1). The actuator heater 42 is activated to atleast partially melt the actuator 50 and/or otherwise increase theflowability of at least the external surfaces of the actuator 50 whilethe actuator 50 remains sealably engaged with the surfaces of thechannel 20. The first gas source 40 a is activated (for example, byactivating the adjacent gas source heater 41) to release gas into thechannel 20 toward the first end 26 and drive the actuator 50 from itsfirst or open position (shown in FIG. 1) to its second or closedposition between the entrance orifice 31 and the exit orifice 32 of thefluid passageway 30. The actuator 50 halts when it reaches the secondunwetted region 25 b, due to very strong capillary forces at theinterface between the actuator 50 and the second unwetted region 25 b.The actuator heater 42 is then deactivated to solidify the actuator 50in its closed position with the actuator 50 sealed against the surfaces21, 22 and 23 of the channel 20. The gas source heater 41 is thendeactivated and the first gas source 41 a re-absorbs the released gas.

[0024] To open the fluid passageway 30, the actuator 50 is heated asdescribed above is and the second gas source 40 b is activated to drivethe actuator 50 from the closed position to the open position. Theactuator 50 is then allowed to cool to solidify the actuator 50 in theopen position and seal the actuator 50 against the surfaces of thechannel 20. The second gas source 40 b is cooled to allow the gasreleased into the channel 20 to reabsorb to the second gas sources 40 b.In one embodiment, the foregoing steps can be repeated to cycle theactuator 50 back and forth between the open position and the closedposition at a frequency of up to at least 1,000 cycles per second. Inother embodiments, the actuator 50 can be cycled at other frequencieshigher or lower than 1,000 cycles per second.

[0025] In one embodiment, the assembly 10 can be formed in silicon oranother semiconductor substrate using photolithographic masking andetching techniques to define several features of the assembly 10. Forexample, when the gas source heaters 41 and the actuator heater 42include electrical resistance heaters, the heaters 41, 42 can be formeddirectly in the first portion 11 a by first etching cavities toaccommodate the heaters and then depositing or otherwise disposing inthe cavities a conductive material that achieves the desired temperaturewhen an electrical current is applied to the conductive material.Alternatively, the heaters 41 and 42 can be positioned in the secondportion 11 b using similar techniques.

[0026] The channel 20 can also be formed in the first portion 11 a usingan etching technique. In one embodiment, the bottom surface 21 and theside surfaces 22 of the channel 20 (including the wetted region 24 andthe non-wetted regions 25 a and 25 b) can then be oxidized. Next, thewetted region 24 can be coated with a metal adhesion layer, such aschromium, followed by a noble metal film, such as platinum, or anotherwettable metal material. The top surface 23 of the channel 20 (in thesecond portion 11 b) can be processed in a generally similar manner.

[0027] Before the second portion 11 b is attached to the first portion11 a, the actuator 50 is positioned in the wetted region 24 of thechannel 20. In one embodiment, the volume of material forming theactuator 50 is selected to span the channel 20 from one side surface 22to the other and from the bottom surface 21 to the top surface 23 whenthe body second portion 11 b is attached to the first portion 11 a.However, the volume of actuator material does not occupy the entirewetted region 24 to allow for movement of the actuator 50 back and forthbetween the open and closed positions. When the gas sources 40 includemetal hydrides, they can be deposited directly in the ends 26 and 27 ofthe channel 20. Alternatively, the hydride or other gas source 40 can bepre-formed and positioned in the channel 20. The second portion 11 b ofthe body 11 can then be attached to the first portion 11 a in an inertor a reducing environment to promote adhesion between the two portions.

[0028] In one embodiment, the actuator 50 can be disposed in the channel20 using a conventional etch and photomask process. For example, thematerial forming the actuator 50 can be deposited directly into thechannel 20 (and, in one embodiment, over other parts of the firstportion 11 a). A layer of photoresist material can be applied to theactuator material and a positive or negative mask can be used toeliminate the photoresist from all regions except a region that definesthe outline of the actuator 50. The remaining photoresist shields theportion of the actuator material that defines the actuator 50 and theexcess actuator material is etched away using conventional etchants.

[0029]FIG. 2 illustrates an alternate method for disposing the actuator50 in the channel 20 in accordance with another embodiment of theinvention. This method may be suitable where it is difficult to removethe excess actuator material with an etching process. In one aspect ofthis embodiment, a spacer layer 62 and a resist layer 60 are disposed onthe bottom surface 21 of the channel 20 and on other parts of the firstportion 11 a. An aperture 61 is formed in the resist layer 60 and thespacer layer 62 and is aligned with an actuator deposition region 56 inthe channel 20. The spacer layer 62 can be undercut (for example, byetching the spacer layer 62) so that the resist layer 60 has anoverhanging portion 63 that faces directly toward the bottom surface 21of the channel 20. The actuator material 55 is deposited on the firstportion 11 a to form the actuator 50 in the actuator deposition region56 and an excess portion 57 of the actuator material 55 on the resistlayer 60. The excess portion 57 and the resist layer 60 are then removedby dissolving the spacer layer 62 with an appropriate solvent. Theoverhanging portion 63 can reduce the likelihood for “bridging” betweenthe actuator 50 and spacer layer 62, and can also provide an accesschannel for the solvent.

[0030]FIG. 3A is a cross-sectional side view of a portion of theassembly 10 described above with reference to FIG. 1 immediately afterattaching the second portion 11 b to the first portion 11 a. In oneaspect of this embodiment, the actuator 50 is initially disposed in theactuator channel 20 in a solid state to extend over a portion of thewetted region 24 and the first unwetted region 25 a. The actuator 50projects upwardly from the bottom surface 21 of the channel 20, but doesnot initially contact the top surface 23. When an electrical current isapplied to the actuator heater 42, the actuator 50 liquifies. Becausethe surface tension between the liquified actuator 50 and the firstunwetted region 25 a is substantially higher than between the liquifiedactuator 50 and the wetted region 24, the actuator 50 retracts from theunwetted region 25 a to form a meniscus at the interface between thewetted region 24 and the unwetted region 25 a, as shown in FIG. 3B. In afurther aspect of this embodiment the liquified actuator 50 wicksupwardly along the side surfaces 22 of the channel 20 to engage the topsurface 23. Accordingly, the actuator 50 can fill the entirecross-sectional flow area of the channel 20 (as shown in FIG. 1) afterits initial liquifaction. When the actuator 50 cools and solidifies, itcan form a sealed interface with the surfaces of the channel 20 toprevent fluid in the fluid passageway 30 (FIG. 1) from escaping past theactuator 50 toward the ends 26, 27 (FIG. 1) of the channel 20. In oneembodiment, the actuator 50 can have a length approximately equal totwice its height, and in other embodiments, the actuator 50 can haveother dimensions, depending on the dimensions of the channel 20.

[0031] In still further embodiments, the actuator 50 can be disposed inthe channel 20 in other manners. For example, the actuator 50 caninitially be positioned to reside entirely within the wetted region 24,rather than extending into the first unwetted region 25 a. The actuator50 then wicks up the side surfaces 22 to the top surface 23 of thechannel upon being heated, as described above. Alternatively, theactuator 50 can be initially disposed in the channel 20 in a liquidform, provided that the environment in which the assembly 10 is formedhas a temperature above the melting point of the actuator 50.

[0032] One feature of an embodiment of the assembly 10 described abovewith reference to FIGS. 1-3 is that the channel 20 and the actuator 50can be made extremely compact by forming these and other elements of theassembly 10 directly in the body 11. Accordingly, the overall dimensionsof the assembly 10 can be suitable for many subminiature applications.For example, (referring now to FIG. 1) the channel 20 can have a width“W” of from about one micron to about five microns and a length “L” offrom about two microns to about 50 microns. In other embodiments, thedimensions of the channel 20 can be smaller, provided that thetechniques for forming the channel 20 and other components of theassembly 10 are compatible with the reduced dimensions. Conversely, thechannel 20 and the actuator 50 can be larger in still furtherembodiments provided that (a) the actuator 50 can remain in contact withthe surfaces 21, 22, and 23 of the channel 20 when in a liquid state,and (b) the actuator 50 does not develop so much momentum as it moveswithin the channel 20 that it crosses from the wetted region 24 intoeither of the unwetted regions 25 a, 25 b.

[0033] Another feature of an embodiment of the assembly 10 describedabove with reference to FIGS. 1-3 is that the actuator 50 is in a liquidor otherwise flowable state when it is in motion, and can be solidifiedwhen at rest. An advantage of this feature is that the actuator 50 canrequire less force than some conventional actuators to move betweenpositions because of the relatively low friction between the liquidactuator 50 and the surfaces of the channel 20. Another advantage isthat the actuator 50 may be less susceptible to accidental actuation(for example, in a high pressure or high acceleration environment)because the actuator 50 will not move unless it is heated. Still anotheradvantage is that the actuator 50 can form a strong, liquid-tight and/orgas-tight bond with the surfaces of the channel 20 (generally similar tothe bond between solder and soldered wires) when the actuator 50 is inthe solid state. Accordingly, the actuator 50 can withstand highpressures when in the solid state.

[0034] Still another advantage of an embodiment of the actuator 50 isthat the surface tension and the volume free energy of the actuator actto minimize the length of the actuator 50 and preserve the integrity ofthe actuator when the actuator is in a liquid state. Accordingly, theactuator 50 can withstand relatively high pressures (such as thepressure of the fluid acting or the actuator 50 through the entranceorifice 31) without becoming fragmented, even when the actuator is in aliquified or partially liquified state.

[0035] Yet another feature of an embodiment of the assembly 10 is thatthe actuator 50 can perform functions other than the valve functionsdescribed above with reference to FIGS. 1-3. For example, in oneembodiment, the heaters 41 and 42 can be eliminated and the actuator 50can move when the temperature of its environment increases by an amountsufficient to liquify the actuator 50 and release gas from one of thegas sources 40. Accordingly, the actuator 50 can be coupled to a firesuppression system or other heat-activated device. In other embodiments,the actuator 50 can be operatively coupled to elements other than afluid channel, such as electrical contacts of a fuse or a relay totransmit linear motion to the other elements. In other embodiments, theactuator 50 can have other functions and/or can be operatively coupledto other devices.

[0036]FIG. 4 is a top isometric view of a portion of an assembly 110having an actuator 150 configured in accordance with another embodimentof the invention. In one aspect of this embodiment, the assembly 110 caninclude a body 111 having a first portion 11 a with a channel 120 and asecond portion 111 b generally similar to the first portion 11 a andsecond portion 11 b described above with reference to FIGS. 1-3B. Theactuator 150 is disposed in the channel 120 and is movable within thechannel (as indicated by arrows “C” and “D”) between a first position(shown in FIG. 4) and a second position. In the first position, theactuator 150 allows a fluid to pass through a fluid passageway 130 froman entrance orifice 131 across the channel 120 to an exit orifice 132.In the second position, the actuator 150 blocks the motion of fluid fromthe entrance orifice 131 to the exit orifice 132, as will be describedin greater detail below.

[0037] In one embodiment, the actuator 150 includes two flowableportions 151 positioned at opposite ends of a non-flowable sliderportion 152. The flowable portions 151 operate in a manner generallysimilar to that described above with reference to FIGS. 1-3 to liquifyand move the actuator 150 over a wetted region 124 of the channel 120positioned between a first unwetted region 125 a and a second unwettedregion 125 b. Conversely, the slider portion 152 can remain in a solidstate throughout the operation of the actuator 150 in one embodiment.

[0038] In one aspect of this embodiment, the slider portion 152 includesa groove 158 that extends across the width “W” of the channel 120. Thegroove 158 is aligned with the entrance orifice 131 and the exit orifice132 when the actuator 150 is in the open position to allow fluid to passfrom the entrance orifice 131 to the exit orifice 132. The groove 158 isoffset from the entrance orifice 131 and the exit orifice 132 when theactuator 150 is in the closed position to prevent the fluid from passingfrom the entrance orifice 131 to the exit orifice 132. As the sliderportion 152 moves back and forth between the open and closed positions,the flowable portions 151 of the actuator 150 can seal against thesurfaces of the channel 120 and the slider portion 152 to prevent thefluid from escaping past the actuator 150 toward opposite ends 126 and127 of the channel 120.

[0039] In one embodiment, the slider portion 152 can be formed from ahydrogenated amorphous silicon carbide. In one aspect of thisembodiment, the slider portion 152 can be formed by depositing in thechannel 120 an Si_(x)C_(y):H compound by plasma enhanced chemical vapordeposition (PECVD). The adhesive forces between the resulting sliderportion 152 and the surfaces of the channel 120 can be reduced in oneembodiment by lowering the temperature at which the PECVD process occursand/or by adding CF₄ to the plasma to form a Si_(x)C_(y)F_(z):H film.The resulting carbide slider portion 152 can be mechanically polished toproduce a flat surface for mating with a top surface 123 of the channel120 defined by the second portion of the body 111. The groove 158 can beformed in the slider portion 152 by a reactive ion etching process,which can also be used to remove any extraneous carbide in the channel120. In other embodiments, the slider portion 152 can be formed fromother materials and/or by other processes.

[0040] One feature of an embodiment of the assembly 110 described abovewith reference to FIG. 4 is that the slider portions 152 can isolate thefluid passing through the passage 130 from contact with the flowableportions 151. An advantage of this feature is that the assembly 110 canbe used to control the flow of fluids that are not compatible with thematerials forming the flowable portions 151 of the actuator 150. Anotheradvantage of this feature is that the slider portion 152 can isolate thefluid in the passageway 130 from contact with the wetted region 124 ofthe channel 120. Accordingly, the assembly 110 can reduce the likelihoodfor oxidizing or otherwise contaminating the wetted region 124.

[0041]FIG. 5 is a schematic illustration of a valve assembly 280configured to incrementally vary a flow of fluid in accordance withanother embodiment of the invention. In one aspect of this embodiment,the valve assembly 280 can include four multiplexed valves 210 (shown asvalves 210 a-210 d), each configured in a manner generally similar tothe assembly 10 or the assembly 110 described above with reference toFIGS. 1-4. Accordingly, each valve 210 has a entrance orifice 231, anexit orifice 232, and an actuator (not shown in FIG. 5) that can moveback and forth between the entrance orifice 231 and the exit orifice 232to open and close fluid communication between each pair of entrance andexit orifices. In a further aspect of this embodiment, each valve 210can have a separate gas source for driving each valve actuator.Alternatively, a pair of gas sources (one for each direction of travelof the actuators) can be coupled to all the valves 210 a-210 d, withonly selected valve actuators moving, depending on which actuatorheaters are activated.

[0042] In a further aspect of this embodiment, each entrance orifice 231can be coupled to an entrance manifold 282 which is in turn coupled to asource 284 of fluid. Each exit orifice 232 can be coupled to an exitmanifold 283 which can in turn be coupled to downstream devices (notshown). Alternatively, the valves 210 a-210 d can be coupled to isdifferent sources 284, for example, to mix fluids from the differentsources.

[0043] In still another aspect of this embodiment, each valve 210 canhave a different flow capacity. For example, the first valve 210 a canhave a flow capacity of one flow rate unit, the second valve 210 b canhave a flow capacity of two flow rate units, the third valve 210 c canhave a flow capacity of three flow rate units, and the fourth valve 210d can have a capacity of four flow rate units. By selectively openingone or more of the valves 210 a-210 d, the valve assembly 280 can allowa fluid flow having any integer value of from zero flow rate units to 10flow rate units to pass from the entrance manifold 282 to the exitmanifold 283. Accordingly, while each individual valve 210 does notincrementally adjust the flow of fluid from the entrance manifold 282 tothe exit manifold 283, the combination of valves 210 can provide such anincremental adjustment. In other embodiments, other combinations ofvalves and valve capacities can be used to provide more or fewerincremental flow rates. In one embodiment, the valves 210 a-210 d can beformed in a single substrate (such as a semiconductor substrate) oralternatively, one or more of the valves 210 a-210 d can be formed in aseparate substrate.

[0044] From the foregoing, it will be appreciated that specificembodiments of the invention have been described herein for purposes ofillustration, but that various modifications may be made withoutdeviating from the spirit and scope of the invention. Accordingly, theinvention is not limited expect as by the appended claims.

1. A valve assembly, comprising: a valve body having a piston channelwith a first end, a second end spaced apart from the first end and anorifice between the first and second ends; a piston disposed in thepiston channel and movable within the piston channel from a firstposition with the piston spaced apart from the orifice to a secondposition with the piston blocking the orifice when at least a portion ofthe piston engaged with surfaces of the piston channel is in a flowablestate; and a piston heater positioned proximate to the piston channel toheat the piston from a solid state to a flowable state.
 2. The valveassembly of claim 1 wherein the piston includes a non-flowable sliderportion having a first end, a second end opposite the first end, and agroove between the first and second ends, the groove being aligned withthe orifice when the piston is in the first position and offset from theorifice when the piston is in the second position, and further whereinthe piston includes a first flowable portion adjacent to the first endof the slider portion and a second flowable portion adjacent to thesecond end of the slider portion.
 3. The valve assembly of claim 1wherein the piston channel has a first region with a first surfacecharacteristic and at least one second region adjacent to the firstregion and having a second surface characteristic different than thefirst surface characteristic, and further wherein the piston includes apiston material having a first surface tension when the piston materialis in a flowable state and positioned adjacent to the first region ofthe channel, the piston material having a second surface tension greaterthan the first surface tension when the piston material is in a flowablestate and positioned adjacent to the second region of the channel. 4.The valve assembly of claim 1 wherein the valve body includes a siliconsubstrate and the piston channel is formed in the silicon substrate. 5.The valve assembly of claim 1 wherein the piston channel has a widthtransverse to a direction of travel of the piston of from about 1.0micron to about 5.0 microns or less and a length generally aligned withthe direction of travel of from about 2.0 microns to about 50.0 micronsor less.
 6. The valve assembly of claim 1 wherein the piston channel hasfour wall surfaces and the valve body includes a first portion havingthree of the wall surfaces, the valve body further including a secondportion bonded to the first portion and having the fourth wall surface.7. The valve assembly of claim 1 wherein the piston channel has achannel wall surface with a first region and at least one second regionadjacent to the first region, the first region including a noble metaland the second region including an oxide, and further wherein the pistonincludes a solder material having a first surface tension when thesolder material is in a flowable state and adjacent to the first regionof the channel surface, the solder material having a second surfacetension greater than the first surface tension when the solder materialis in a flowable state and adjacent to the second region of the channel.8. The valve assembly of claim 1 wherein the piston includes a soldermaterial.
 9. The valve assembly of claim 1 wherein the piston channelhas a first end and a second end and the piston is positioned betweenthe first and second ends, and wherein the assembly further comprises afirst gas source coupled to the piston channel toward the first end anda second gas source coupled to the piston channel toward the second endto move the piston between the first and second positions.
 10. The valveassembly of claim 1, further comprising a resistive heater formed in thevalve body adjacent to the piston channel and configured to at leastpartially liquify the piston.
 11. The valve assembly of claim 1 whereinthe piston channel is a first piston channel, the orifice is a firstorifice, and the piston is a first piston, and wherein the valve bodyhas a second piston channel with a second orifice and a second pistonmovable within the second piston channel between a third position and afourth position, the first orifice being coupled to a first fluidpassageway, the second orifice being coupled to a second fluidpassageway arranged in parallel with the first fluid passageway tocontrol a flow of fluid through the passageways.
 12. The actuatorassembly of claim 1 wherein the valve body further includes a ventchannel coupled to the piston channel to vent gas directed into thechannel against the piston.
 13. An actuator assembly, comprising: anactuator body having an actuator channel with a first end and a secondend spaced apart from the first end; an actuator disposed in theactuator channel and movable when in a flowable state from a firstposition in the actuator channel to a second position in the actuatorchannel, the actuator being operatively coupleable to an actuateddevice; and a heater positioned proximate to the actuator channel toheat the actuator from a solid state to a flowable state.
 14. Theactuator assembly of claim 13 wherein the heater includes a resistiveheater integrated with the actuator body and configured to liquify atleast a portion of the actuator.
 15. The actuator assembly of claim 13wherein the actuator includes a solder material.
 16. The actuatorassembly of claim 13 wherein the actuator channel is defined by achannel material, and further wherein the channel material has a firstmelting point that is higher than a second melting point of theactuator.
 17. The actuator assembly of claim 13, wherein the actuatorbody further includes a fluid passageway having an orifice in fluidcommunication with the actuator channel and wherein the fluid passagewayis operatively coupled to a source of fluid to control a flow of fluidfrom the source when the actuator moves from the first position to thesecond position.
 18. An actuator assembly, comprising: an actuator bodyhaving an actuator channel with a first end and a second end spacedapart from the first end, the actuator channel having a channel surfacewith a first region having a first surface characteristic and positionedadjacent to at least one second region having a second surfacecharacteristic different than the first surface characteristic; and anactuator disposed in the actuator channel and movable when in a flowablestate from a first position in the actuator channel to a second positionin the actuator channel, the actuator including a flowable materialhaving a first surface tension when the actuator is in a flowable stateand positioned adjacent to the first region of the channel, the flowablematerial having a second surface tension greater than the first surfacetension when the actuator is in a flowable state and positioned adjacentto the second region of the channel.
 19. The actuator assembly of claim18 wherein the second region is one of two second regions having thesecond surface characteristic, with the first region positioned betweenthe two second regions.
 20. The assembly of claim 18 wherein the channelsurface in the first region includes at least one of platinum, rhodium,palladium and gold.
 21. The assembly of claim 18 wherein the channelsurface in the second region includes at least one of an oxide and anitride.
 22. The assembly of claim 18 wherein the actuator channel isdefined by a channel wall, and further wherein a surface of the channelwall in the second region includes at least one of silicon dioxide,aluminum oxide and silicon nitride.
 23. The assembly of claim 18 whereinthe actuator includes at least one of lead, tin, bismuth, cadmium,selenium, thallium and zinc.
 24. The actuator assembly of claim 18,further comprising a heater positioned proximate to the actuator channelto heat the actuator from a solid state to a flowable state.
 25. Theactuator assembly of claim 18 wherein the actuator includes a slidermember positioned between first and second portions of the flowablematerial.
 26. The actuator assembly of claim 18 wherein the actuatorbody includes an orifice in fluid communication with the actuatorchannel and coupleable to a source of fluid, and further wherein theactuator includes a slider member positioned between first and secondportions of the flowable material, the slider member having a groovealigned with the orifice when the actuator is in the first position andoffset from the orifice when the actuator is in the second position. 27.The actuator assembly of claim 18 wherein the actuator includes a slidermember positioned between first and second portions of the flowablematerial, and wherein the slider member includes a hydrogenatedamorphous silicon carbide.
 28. A microvalve assembly, comprising: asilicon valve body having a piston channel with a first end, a secondend spaced apart from the first end, and an orifice between the firstand second ends, the piston channel having a channel surface with afirst region coated with a first coating and positioned between twosecond regions with each second region coated with a second coating; apiston in the piston channel and movable between a first position withthe piston blocking the orifice and a second position with the pistonspaced apart from the orifice, the piston including a piston materialhaving a first surface tension when the piston is in a liquid state andadjacent to the first coating of the channel, the piston material havinga second surface tension greater than the first surface tension when thepiston is in a liquid state and adjacent to the second coating of thechannel; a first hydride gas source coupled to the piston channel towardthe first end; a second hydride gas source coupled to the piston channeltoward the second end; a first hydride heater thermally coupled to thefirst hydride gas source to release hydrogen from the first hydride gassource; a second hydride heater thermally coupled to the second hydridegas source to release hydrogen from the second hydride gas source; and apiston heater positioned proximate to the piston channel to heat thepiston from a solid state to a liquid state.
 29. The assembly of claim28 wherein the piston includes at least one of lead, tin, bismuth,cadmium, selenium, thallium and zinc, the first coating includes atleast one of platinum, rhodium, palladium and gold, and the secondcoating includes at least one of an oxide and a nitride.
 30. A methodfor manufacturing an actuator, comprising: forming in a substrate achannel having a first region and at least one second region adjacent tothe first region, the first region having a first surface characteristicand the second region having a second surface characteristic differentthan the first surface characteristic; and positioning an actuator inthe channel, at least a portion of the actuator having a first surfacetension when in a flowable state and contacting the first region, theactuator having a second surface tension when in a flowable state andcontacting the second region, with the second surface tension greaterthan the first surface tension, the actuator being operativelycoupleable to an actuated device.
 31. The method of claim 30 wherein thesecond region is one of two second regions, and wherein the methodfurther comprises forming the channel to have another second region withthe first region positioned between the two second regions.
 32. Themethod of claim 30, further comprising selecting a material of the firstregion to include at least one of platinum, rhodium, palladium and gold.33. The method of claim 30, further comprising selecting a material ofthe second region to include at least one of an oxide and a nitride. 34.The method of claim 30, further comprising selecting a material of thesecond region to include at least one of silicon dioxide, aluminum oxideand silicon nitride.
 35. The method of claim 30, further comprisingselecting a material forming the actuator to include at least one oflead, tin, bismuth, cadmium, selenium, thallium and zinc.
 36. The methodof claim 30, further comprising positioning a heater proximate to thechannel to heat the actuator from a solid state to a flowable state. 37.The method of claim 30, further comprising: forming the actuator toinclude a slider member positioned between first and second portions ofa flowable material; and selecting the slider member to include ahydrogenated amorphous silicon carbide.
 38. The method of claim 30,further comprising forming an orifice in fluid communication with thechannel, the orifice being coupleable to a source of fluid, the orificebeing blocked by the actuator when the actuator is in the secondposition to at least restrict the fluid from flowing through theorifice, the orifice being open to the channel when the actuator is inthe second position.
 39. The method of claim, further comprising:forming an orifice in fluid communication with the actuator channel, theorifice being coupleable to a source of fluid; and forming the actuatorto include a slider member positioned between first and second portionsof a flowable material, the slider member having a passage aligned withthe orifice when the actuator is in the first position and offset fromthe orifice when the actuator is in the second position.
 40. A methodfor manufacturing an actuator, comprising: forming a channel in asubstrate; positioning an actuator in the channel, the actuator beingmovable within the channel between a first position and a secondposition when the actuator is in a flowable state; and disposing anactuator heater adjacent to the channel, the actuator heater beingconfigured to at least partially liquify the actuator.
 41. The method ofclaim 40 disposing the actuator heater includes integrating a resistiveheater with the substrate.
 42. The method of claim 40, furthercomprising selecting the actuator to include a solder material.
 43. Themethod of claim 40, wherein positioning an actuator in the channelincludes depositing in the channel by chemical vapor deposition amaterial forming the actuator.
 44. The method of claim 40, furthercomprising selecting a material defining the channel to have a firstmelting point that is higher than a second melting point of theactuator.
 45. A method for manufacturing a flow valve, comprising:forming a channel having channel surfaces in a first silicon substrate;disposing a first coating on a first region of the channel surfaces;disposing a second coating on two second regions of the channel surfacesadjacent to opposite ends of the first region; positioning a piston inthe channel, the piston having a first surface tension when in a liquidstate and contacting the first coating, the piston having a secondsurface tension when in a liquid state and contacting the secondcoating, with the second surface tension greater than the first surfacetension; forming a fluid flow channel in the first silicon substrate,the flow channel having an orifice in fluid communication with thechannel; sealing the piston in the channel by attaching to the firstsilicon substrate a second silicon substrate having a surface facingtoward the piston; forming a piston heating element in at least one ofthe first and second silicon substrates to heat the piston to a liquidstate; and coupling a first hydrogen source to one end of the channeland coupling a second hydrogen source to an opposite end of the channel.46. The method of claim 45 wherein positioning a piston in the channelincludes depositing in the channel by chemical vapor deposition amaterial forming the piston.
 47. The method of claim 45 whereinpositioning a piston in the channel including depositing a non-flowablematerial in the channel, disposing a first volume of a flowable materialin the channel adjacent to one end of the non-flowable material, anddisposing a second volume of the flowable material in the channeladjacent to an opposite end of the non-flowable material, thenon-flowable material remaining in a solid state when the piston heatingelement is activated, the flowable material at least partiallyliquifying when the piston heating element is activated.
 48. The methodof claim 45 wherein forming a channel includes forming a depression inthe first silicon substrate, the depression having a length aligned witha direction of travel of the piston of from about two microns to aboutfifty microns or less, the depression having a width transverse to thelength of from about one micron to about five microns or less.
 49. Amethod for controlling an actuator, comprising: heating the actuator inan actuator channel from a solid state to a flowable state; moving theactuator within the actuator channel from a first position to a secondposition with a flowable portion of the actuator in contact withsurfaces of the actuator channel; and cooling the actuator to solidifythe actuator in the second position.
 50. The method of claim 49 furthercomprising liquifying the actuator before moving the actuator from thefirst position to the second position.
 51. The method of claim 49wherein moving the actuator includes applying pressurized gas to theactuator.
 52. The method of claim 49 wherein moving the actuatorincludes: heating a first hydride material to release hydrogen into theactuator channel on a first side of the actuator to drive the actuatorin a first direction; heating a second hydride material to releasehydrogen into the actuator channel on a second side of the actuator todrive the actuator in a second direction opposite the first direction;and cooling at least one of the first and second hydride materials toreabsorb at least some of the hydrogen.
 53. The method of claim 49,further comprising covering an orifice to at least restrict a flow offluid through the orifice by moving the actuator from the first positionto the second position.
 54. The method of claim 49 wherein heating theactuator includes heating a portion of the actuator that includes atleast one of lead, tin, bismuth, cadmium, selenium, thallium and zinc.55. A method for controlling an actuator, comprising: moving a flowableactuator along a surface of a first region of an actuator channel from afirst position to a second position, the actuator having a first surfacetension when in the first region; halting motion of the flowableactuator at the second position by engaging the actuator with a surfaceof a second region of the channel, the actuator having a second surfacetension greater than the first surface tension when engaged with thesecond region; and operatively coupling the actuator to an actuateddevice.
 56. The method of claim 55 wherein moving a flowable actuatorincludes moving an actuator that includes at least one of lead, tin,bismuth, cadmium, selenium, thallium and zinc.
 57. The method of claim55 wherein moving a flowable actuator includes moving the actuator overa surface that includes at least one of platinum, rhodium, palladium andgold.
 58. The method of claim 55, wherein halting motion of the flowableactuator includes engaging the actuator with at least one of an oxidesurface and a nitride surface.
 59. The method of claim 55, furthercomprising: heating the actuator from a solid state to an at leastpartially flowable state before moving the actuator; and cooling theactuator to solidify the actuator when the actuator has moved from thefirst position to the second position.
 60. The method of claim 55wherein operatively coupling the actuator to an actuated device includescoupling a fluid flow passage to the channel with the actuator blockingfluid flow through the flow passage when in the second position.
 61. Amethod for controlling a flowable substance, comprising: liquifying apiston in a piston channel by heating the piston; heating a hydridesource to release hydrogen gas into the piston channel; driving thehydrogen gas against the piston to move the liquified piston within afirst region of the piston channel from a first position with the pistonspaced apart from an orifice to a second position with the liquifiedpiston blocking the orifice, the liquified piston having a first surfacetension when in the first region of the piston channel; halting motionof the liquified piston within the channel by engaging the liquifiedpiston with a second region of the piston channel, the liquified pistonhaving a second surface tension greater than the first surface tensionadjacent to the second region of the piston channel; and solidifying thepiston in the second position by cooling the piston.
 61. The method ofclaim 61 wherein the piston is a first piston in a first piston channeland the orifice is a first orifice having a first flow capacity andcoupled to a fluid source, and wherein the method further comprisesselectively liquifying the first piston in the first piston channeland/or a second piston in a second piston channel having a secondorifice with a second flow capacity different than the first flowcapacity and coupled to the fluid source; and selectively moving thefirst piston and/or the second piston to control a rate of fluid flowfrom the fluid source.
 62. The method of claim 61, further comprisingmoving the piston back and forth between the first position and thesecond position at a rate of up to at least 1,000 cycles per second.